1. Technical Field
The present invention relates to a technology for decoding a compression coded video signal.
2. Description of the Related Art
As standards for the compression coding scheme for moving image data, there exist H.262/MPEG-2 (hereinafter called MPEG-2), H.264/MPEG4-AVC (hereinafter called H.264), and the like. MPEG-2 was standardized by ISO/IEC to encode television signals in an interlaced format at around 6 Mbit/s and encode HDTV signals at about 20 Mbit/s. The video part of MPEG-2 (ISO/IEC 13818-2) has been published as common text (ITU-T H.262) with ITU-T. In contrast, H.264 is assumed to be widely used from low bit rate applications such as mobile phones to high bit rate applications such as HDTV and was standardized by a joint group JVT of ITU-T and ISO/IEC.
Video compression coding technology of these standards comprises a motion-compensated inter-image difference coding technique, an orthogonal transform technique such as a discrete cosine transform (DCT), a quantization/inverse quantization technique, an entropy coding technique such as variable-length coding, and so on.
In video compression coding based on these standards, in order to achieve high efficiency coding, quantization is performed where a video signal is divided by a certain value and where the remainder is rounded. When decoding video compression coded data, data rounded by quantization is not completely restored, and thus degradation in image quality such as block distortion or mosquito distortion will appear if the divisor is large.
As techniques to reduce the quantization noise influence in a decoding apparatus, there have been a post-filtering process, a loop filtering process, and the like. As to the loop filtering process, for example, deblocking filtering is specified as standard in H.264. As to the post-filtering process, there is a technique shown in, e.g., Japanese Patent Application Laid-Open Publication No. 2006-157938 (Reference 1).